Recent incidents in the field of orthodontics have made practitioners aware of safety hazards surrounding the use of various equipment. Especially potentially hazardous are extra-oral appliances, i.e., those worn outside the mouth or in conjunction with equipment outside the mouth. In particular, facebows and low and high pull headgear have been found to be a source of potential injury to the patient, since such appliances have heretofore been designed so that undesirable pulling of the facebow away from the patient's mouth "loads" the appliance in much the same manner as a slingshot. Additionally, if the ends of the inner bow are drawn sufficiently far forward, they will slip out of the buccal tubes usually employed to support them and become misaligned with the tube openings, thereby presenting themselves as a pair of pointed, dangerous protrusions. If the facebow is pulled out sufficiently, the ends of the inner bow may be in a position to do serious damage to the inner mouth, tongue, gums or even the lips, face and eyes. At least one such incident has been reported which resulted in blinding the patient.
Prior art solutions to the problem of eliminating dangers associated with undesired tampering with the facebow or undesirable pulling on the headgear tensioning means include various methods, depending upon the type of tensioning apparatus being used (spring, rubber band or elastic strap) and upon the individual preference of the orthodontist. One approach is to permanently tie the inner bow in place with steel ligature wire. This method presents some hygiene problems but causes more concern because undesired pulling could cause the facebow to be severly deformed. If the patient should continue wearing a deformed facebow, it could cause harm to the patient in addition to being detrimental to the intended orthodontic treatment.
Because of the obvious disadvantages and dangers of permanently affixing the inner bow to the buccal tubes, removal systems which avoid the dangers enumerated above are much more desirable. Several removable systems are presently available to the orthodontic practitioner, including but not limited to the following:
One removable headgear system, described in U.S. Pat. No. 3,903,604, uses two different devices for locking the inner bow into the buccal tube. These mechanisms appear to satisfy the requirement that the device be capable of selective removal by either the orthodontist or the patient; however, the apparatus described is complex, expensive to manufacture and does not permit adjusting the length of the inner bow members for different patients. This presents a significant manufacturing problem and an inventory problem for the practitioner, since a very large selection of sizes is required in order to accomodate the average size distribution of patients.
A second approach attempts to limit extension of the tensioning means. While theoretically intended to limit the travel of the inner bow members in the bucca tubes, the practical result is at best confinement of the inner bow members to the oral cavity. These devices are of limited value because they do not prohibit undesired removal of the inner bow members from the buccal tube; the serious danger of a "slingshot" effect caused by the tensioning means propelling the ends of the facebow into soft tissues of the oral cavity is thus not eliminated. The reason for the failure of these travel limiting devices is the fact that it is impossible to eliminate displacement of the soft tissues of the patient's neck or to control the angle of the patient's head. Both of these factors influence the amount of slack in the tensioning members of the device in relationship to their connection to the outer members of the facebow. These devices may actually be more dangerous because of the false sense of security they provide.
A third approach to assure safety of headgear devices by preventing undesired removal of the bow members is presently available to the profession and provides a breakaway mechanism between the tensioning means and the facebow. This particular mechanism is designed to function on a spring tensioning system, e.g. as described in U.S. Pat. No. 3,526,035, but is not directly adaptable to headgear using other elastic tensioning means. The major advantage of this safety means is that the "slingshot" effect and permanent damage to the semi-rigid portions of the apparatus are both effectively prevented. There are, however, major practical disadvantages associated with this system in addition to its applicability being limited to spring tensioned headgear. First, a large inventory of headgear is required because the system is designed to have a narrow, preset force range to insure proper functioning of the disconnect system. Second, the travel limiting system is not adjustable and provides such limited travel that disconnection may occur while attempting to engage the apparatus. Third, the force adjustment feature, in addition to having a narrow range, allows only discrete rather than continuous adjustments. Finally, the force module is not self-contained which necessitates the manufacture and assemblage of additional parts, making the unit considerably more expensive than non-safety versions of the same apparatus.